The present invention relates to a unique additive system for reducing static friction, i.e., xe2x80x9cstictionxe2x80x9d in molded polyester articles and films. More particularly, the present invention relates to a method for producing low haze, transparent poly(ethylene terepthalate)(PET) preforms, bottles, sheet and thermoformed articles which contain such an additive system and which exhibit improved slip performance. The additive system comprises an effective amount of (i) a fatty acid amide selected from the group consisting of oleyl palmitamide, ethylene bis stearamide, ethylene bis oleomide, and stearyl erucamide; (ii) a partially or fully calcined porous poly(methylsilsequioxane); and (iii) a primary and a secondary antioxidant.
PET homopolymer and copolymers are widely used in rigid packaging applications, but particularly for carbonated soft drinks (CSD) as they can form strong, lightweight bottles with a satisfactory barrier to gas transmission, primarily oxygen and CO2. In the production of such bottles, PET is first moulded into small somewhat condensed shapes known as preforms, which are relatively thick-walled test tubes with a threaded neck finish, to facilitate appropriate closure. The preforms can then be blown into the final bottle shape (a process known as injection stretch blow molding, or ISBM), by being heated under infrared radiation, placed immediately into a mould, and injected with a sudden blast of air. The air blast expands the preform into the shape of the mould. One of the problems encountered in producing preforms and bottles from PET, however, is that these articles exhibit a mutual sticking effect, which can make high speed handling difficult on modern blowing/conveying machines.
The effect of this sticking phenomenon with preforms packed into a box is a lower than optimum packing density and correspondingly higher transportation cost per preform. The effect further manifests itself when unloading these boxes onto a blowing line, where the preforms tend not to flow smoothly into the automatic unscramblers and other register machinery. This can then result in less than optimum preform feed rates to the blowing machine. Bottles sticking together reduce conveying efficiency and hence overall filling speed on a filling line, and create further problems during bottle palletising/depalletising. In sheet manufacture sticking effects create problems in sheet unrolling and cutting after storage, as well as with de-nesting of thermoformed articles.
The exact origin of the observed sticking effect has not been identified, but it may result from static electricity, intermolecular attraction and/or surface roughness.
The present invention resides in the discovery of a unique additive system for polyester polymers which improves the handling performance of articles and sheet products produced from the polymers by reducing the tendency of the articles and sheet products to adhere or stick. The additive system comprises an effective amount of (i) a fatty acid amide selected from the group consisting of oleyl palmitamide, ethylene bis stearamide, ethylene bis oleomide, and stearyl erucamide; (ii) a partially or fully calcined porous poly(methylsilsequioxane); and (iii) a primary and a secondary antioxidant in a ratio of 1:4, respectively.
According to another aspect, the present invention is a method for reducing the sticking effect, i.e., the static friction effect, or xe2x80x9cstictionxe2x80x9d, between molded articles of PET homo- and co-polymers comprising incorporating into the polymer, at the processing stage, pre-compounded or included through a masterbatch, an effective amount of (i) a fatty acid amide selected from the group consisting of oleyl palmitamide, ethylene bis stearamide, ethylene bis oleomide, and stearyl erucamide; (ii) a partially or fully calcined porous poly(methylsilsequioxane); and (iii) a primary and a secondary antioxidant in a ratio of 1:4, respectively.
According to yet another aspect, the present invention is a method for producing a PET molded article, particularly bottles and other containers for carbonated soft drinks and spring water, having a reduced sticking effect which comprises the steps (1) incorporating into the polymer an effective amount of an additive system comprising a fatty acid amide selected from the group consisting of oleyl palmitamide, ethylene bis stearamide, ethylene bis oleomide, and stearyl erucamide; (ii) a partially or fully calcined porous poly(methylsilsequioxane); and (iii) a primary and a secondary antioxidant in a ratio of 1:4 at any point before molding, and then (2) molding the polymer.
The additive system imparts unexpectedly improved handling properties to transparent preforms, bottles, sheet and thermoformed articles produced from PET resin without affecting the resins""s ability to consistently meet strict specifications with respect to color, taste, odor, feel and toxicity in finished bottles.